1. Field of the Invention
This invention relates generally to computer disk array subsystems used for storing data, and particularly to interfaces between a disk array subsystem and a small computer system. More specifically, this invention relates to an improved disk array subsystem that incorporates a disk drive interface allowing disk drives to be removed and inserted while the system is operating.
2. Description of the Related Art
Within the computer industry and more specifically within the computer data storage field, multiple data storage units are often coupled as an array to provide increased data storage capability. In addition to increasing the data storage size, these devices also increase the speed at which data can be stored and accessed by spreading a block of data among several storage units. For example, several disk drives within an array subsystem may be used to store a block of data, even though the block of data would fit within one disk drive. By storing the data on multiple disk drives, there is less time spent waiting for mechanical movement of read/write heads to a different disk track, or waiting for rotation of the storage media itself. Instead, data is read in a parallel fashion from multiple disks to allow faster data access. In this manner, data can be read faster, thus reducing or eliminating time spent in computer wait cycles.
The disk storage devices that use the industry standard small computer system interface (SCSI) are referred to as SCSI devices. Multiple disk storage devices are commonly referred to as a SCSI disk array.
During operation of a SCSI disk array subsystem, one of the disk drive units may occasionally need to be replaced. In order to replace a disk drive in a conventional disk array system, it is usually necessary to power down the entire system, remove the disk drive, insert a new one and again apply power to the system.
A SCSI disk drive uses what is commonly known as a 50-pin box header connector for interfacing SCSI signals between a disk drive and a computer controller. The box connector has two parallel rows of male pins of equal length that mate with a corresponding box connector with female pins. The power to the SCSI disk is applied via a separate 4-pin connector. Combining these two disk connectors into one connector with equal length pins would solve the quick connect/disconnect problem, but would still cause a system problem. Specifically, because the pins are of equal length, use of a one-piece connector mandates that power be shut down before insertion of the new disk drive unit. Otherwise, upon connection, power and data signals will be sent to the disk drive unit simultaneously which could create data loss or damage to the disk drive unit as a result of power surges or unwanted static discharge. Powering down the disk assembly for replacement of failed disk drive units reduces the amount of time the system is available to the user to perform useful work.
It is thus desired to have a disk array subsystem whereby upon failure of a disk drive unit, the failed unit may be removed and a new unit inserted without powering down the system. In this manner, the time to repair the system is minimized, increasing its availability of the user.
Typically, each disk drive unit within a disk array subsystem has an ID number which corresponds to a physical disk drive slot. The ID number is used for control purposes and to select the disk drive to be involved in the data transfer. When a disk drive fails, the new disk drive must be given the same ID number as the drive that it is replacing. This entails matching certain jumper block settings on a disk drive to an ID number for a particular disk drive slot. Previously, this has been done manually by the operator who is replacing the disk drive. The ID numbers for each disk drive slot of the improved assembly are preset on the backplane. Manually setting the ID number on the new disk drive would increase the amount of time the system was under repair and would also be prone to error which could cause permanent data corruption.
Accordingly, there exists a need for a disk drive subsystem whereby new disk drives can be quickly assigned a new ID number and inserted into the disk array subsystem without powering down the system.